Argument in favour of adopting a theme-based approach in EVS?

Which one among the following is the strongest argument in favour of adopting a theme-based approach in EVS?
(a) It helps in giving a structure to lesson plans and makes teaching more effective.
(b) It helps on making teaching more interesting and activity based
(c) It helps in covering a wide range of concepts issues and skills.
(d) It helps in softening subject boundaries and accessing knowledge holistically.